BDF target design and prototyping

Transcription

1 BDF target design and prototyping 10th International Workshop on neutrino beams & instrumentation (NBI 2017) 18th 22nd September 2017 E. Lopez Sola on behalf of the BDF Project CERN, Engineering Department, STI/TCD

2 Outline Beam Dump Facility Target materials and operation Thermo-structural calculations Material R&D BDF Target prototype 2

3 The Beam Dump Facility Beam Dump Facility target Located in the North Area at CERN Multipurpose fixed target, currently on design phase Dedicated to SHiP experiment in a first stage Explore the domain of hidden particles, such as Heavy Neutral Leptons, dark photons, supersymmetric particles 3

4 BDF target materials Material requirements for the target core High-Z materials To increase the reabsorption of pions and Short interaction length kaons (background for the experiment) Material selection à hybrid target Target/dump 1 st part of the target: TZM à Molybdenum alloy, higher strength and recrystallization temperature than Mo 2 nd part of the target: Tungsten à High-Z and good performance under irradiation Target core dimensions: 250 mm diameter cylinders à contain cascade generated 4 Variable cylinder length à optimized segmentation of the target to minimize the level of stresses. Total target length ~ 1.5 m 12λ Nuclear inelastic scattering length

5 Target materials Cooling Average beam power on target = 320 kw Water cooling needed: 5 mm gap between the blocks 200 m3/h of pressurized water at 20 bar 2 m/s water velocity All the blocks will be cladded with a 1.5 mm Tantalum layer, to protect the core materials from erosion-corrosion effects Ta cladded to the TZM/W cylinders by Hot Isostatic Pressing (HIP) à mechanical and chemical bonding 5

6 BDF target operation Baseline characteristics Proton momentum [GeV/c] 400 Beam intensity [p+/cycle] Cycle length [s] 7.2 Spill duration [s] (slow extraction) 1.0 4*10 13 ppp 1 s Average beam power on target [kw] 320 Average beam power on target during spill [MJ] s High beam power deposited Requires dilution of the beam by the upstream magnets 6

7 BDF target operation Beam dilution optimization: Shape modified from spiral trajectory to circle Multiple turns Maximum temperature after 1 pulse, TZM core Temperature ( C) turn 2 turns 4 turns Time (s) Final configuration: Circular dilution 4 turns in 1 second 7

8 Thermal calculations Energy deposition longitudinal distribution (FLUKA) Max temperature TZM core 190 C Max temperature W core 150 C Max temperature Ta cladding 180 C Temperature limitations in the Ta cladding Ta properties at 180 C reduced significantly with respect to RT High temperatures reached lead to a high level of stresses in the core, cladding and interfaces Thermal fatigue Temperature ( C) TZM core Ta cladding W core ΔT Tantalum ~ 140 C Time (s) 8

9 Structural calculations The stresses reached in the TZM and tungsten cores are acceptable with respect to the material limits for the temperatures reached Maximum principal stress in Tungsten at 150 C HIPed + sintered tungsten tensile strength 20 C-500 C 80 MPa >400 MPa TZM maximum Von Mises equivalent stress = C Strength [MPa] TZM max Von Mises equivalent stress Temp [C] Yield TZM (IAEA) Tensile TZM (IAEA) Tensile TZM stress relieved (Plansee)

10 Structural calculations The level of stresses in the Ta cladding may be critical (bonding interface) Low strength at high temperatures Fatigue effects to be considered (few data at high temperatures) Radiation effects to be taken into account Maximum Von Mises equivalent stress at 180 C = 110 MPa Yield strength at 200 C ~ 70 MPa! Foreseen material characterization campaign and material R&D in order to evaluate the properties of the refractory metals at high temperatures 10

11 Material R&D Solution: use of a tantalum-tungsten alloy, Ta2.5W 2.5% content of W Similar thermal properties to Ta Higher strength, specially at high temperatures Corrosion-erosion resistance Bonding quality to tungsten and TZM expected to be the same Ongoing R&D to study the cladding of Ta2.5W to TZM and W by HIPing Maximum VM equivalent stress Ta2.5W (@180 C) = 110 MPa Yield strength C ~ 200 MPa 11

12 BDF target prototype Design and manufacture of a target prototype Tested in the North Area at CERN during 2018 High intensity beam (up to 1e13 protons) Slow extraction: 1s pulse, 7.2 period Beam non-diluted Dedicated beam during 2 or 3 periods of 10 hours Objective Reproduce the level of temperatures and stresses of the final target Crosscheck the calculations performed PIE foreseen after irradiation 12

13 BDF target prototype Timeline: February 2018: Preparation of the area March 2018: Installation of the target Summer 2018: Testing Prototype target on alignment table Placed on beam during operation (10 hours) Removed from beam for other experiments 13

14 BDF target prototype Reduced scale prototype Diameter reduced to 80 mm Same target length Target core: TZM and W blocks cladded with Ta or Ta2.5W Most critical blocks cladded with Ta2.5W Several iterations to determine the beam intensity and cooling parameters needed to reproduce the state of temperatures and stresses Beam intensity = protons/pulse Total average power on target ~ 20 kw 14

15 Prototype thermal calculations Maximum temperature comparison: prototype vs. final target Temperature ( C) Maximum temperature TZM core Higher temperature reached in prototype Time (s) Prototype target TZM core Final target TZM core Faster core cooling in prototype Temperature ( C) Maximum temperature Ta cladding Time (s) Prototype target Ta cladding Final target Ta cladding Higher temperature reached in prototype Final BDF target BDF target prototype 15

16 Prototype structural calculations Maximum eq. VM Stress TZM core Maximum eq. VM Stress Ta cladding Stress (MPa) Final target TZM core Prototype TZM core Final target Ta cladding Prototype Ta cladding 15% difference % difference Time (s) Stress (MPa) Time (s) Higher stresses in the final target Reasonable approximation of the level of stresses in the core and cladding Limit for higher temperatures à surface temperature à boiling point of water 16

17 Prototype cooling system design Circuit supply pressure: 22 bar Initial design of the water cooling circuit Water flowing on top/bottom of each block and through 5 mm channels between the blocks Non-homogenous velocity Cooling of the circular faces of the cylinders à beam impact P. Avigni (CERN EN/CV) 17

18 Prototype cooling system design Several iterations to optimize the water flow Homogeneous water velocity in the channels High speed à high HTC value (16000 W/m2k) Final choice: guided water flow Blockers on top/bottom of each block Water velocity in the channels = 4 m/s P. Avigni (CERN EN/CV) 18

19 Prototype Instrumentation Beam instrumented with a shielded BTV camera instrumentation Several target blocks instrumented with temperature and strain gauges Instrumentation challenges High levels of radiation High water velocity in the block channels Test-bench foreseen next month Test the instrumentation under high pressure and high speed water Water flow 16 bar 1 kg/s Strain gauge 19

20 Radiation issues PIE High level of radiation challenging for the test O(Sv/h) after 2 months cooling Remote handling of the target Instrumentation connectors + Water connectors PIE foreseen after the operation Characterize beam-induced property changes in the structure and the bonding contact Ta-alloy/core + signs of material weakening ~6 months after operation: (remote) extraction of several target blocks for PIE 20

21 Conclusions A hybrid target of TZM and tungsten cladded with tantalum or a tantalum alloy is considered for the Beam Dump Facility FEM calculations have been performed, showing that tantalum as cladding material would not withstand the stresses induced in the target, justifying the R&D of alternative cladding materials as Ta2.5W. A prototype of the BDF target with reduced dimensions will be tested next year, in order to validate the thermomechanical calculations performed and to carry out a PIE in the radiated target. 21

22 Thank you for your attention! Acknowledgements: M. Calviani, B. Riffaud, L. Zuccalli, P. Avigni, J. Busom, J. Canhoto